Problems with startup and in particular with the so-called heavy start of scraper chain conveyors and winning machines are solved only unsatisfactorily with current pole-changing drive motors and diesel engines with steep characteristic curves inherent to such units. Although a drive system for so-called heavy start and heavy run, respectively, is already available for use with pole-changing (speed-changing) drive motors having an increased torque in low speed steps, this operating method also required especially the elimination of loose chains or sagging chains and shock loads on chains and driving parts of winning machines, scraper chain conveyors and the like.
The use of a power shift gear substantially increases the shock loads, i.e. the torques transmitted to driving parts and chain by the motor in the low step of the power shift gear. In fact, efforts have been made to protect heavy start or heavy run by using variable hydrodynamic couplings but the large space required for the ducts for the operating fluid and for the cooling thereof is a disadvantage.
Moreover, the secondary wheel and the rapidly running gear shaft of the secondary transmission give unfavorable results at least on sudden braking, e.g. on sudden blocking or erratic load increases, because of the high centrifugal force. In addition, a continuous power loss must be accepted due to unavoidable permanent slipping.